90 GEOLOGY OF ILLINOIS. 



1. Light colored, chocolate-brown clay, covered with a thin soil, full of large, unworn gravel, 



not apparently transported, but the undecomposed parts of shaly strata or layers former- 

 ly decayed or rotted into clays, about. 5 feet 



2. Thin bedded, bluish-yellowish strata or layers, breaking with a more or less glassy fracture, 



and in some cases having a vitreous appearance, and in all cases resembling correspond- 

 ing layers in the overlying limestone 15 feet 



3. A layer resembling the last, but heavier bedded and duller colors 6 feet 



4. One and sometimes two layers, separated by clayey shales and loose clays, of heavy bedded, 



massive, very blue limestone, with less conchoidal fracture than corresponding layer in 



Blue limestone 4 feet 



5. Heavy bedded, massive, dull sand colored limestone, very impure, breaks into irregular 



masses, and to the tongue has both a sandy and clayey taste 7 feet 



6. Clays, and clayey and sandy shales 3 feet 



The upper part of all these outcrops, in our judgment, differs in but 

 a slight degree from quarries in the Blue limestone of the same thick- 

 ness. The lower part of the quarries, for four or five feet above and 

 below the blue strata, has a more marked difference. But inasmuch as 

 Professor WHITNEY, and other eminent geologists, class these quarries 

 as the Buff limestone, and inasmuch as the types of characteristic fos- 

 sils are somewhat different, we shall describe and map them in these 

 reports as belonging to this division of the Trenton formation. 



Fossils. The characteristic fossils of the Buff limestone, observed at 

 Bockton, consist of fragments and indistinct traces of fucoids : Cephalo- 

 poda, of the genus Orthoceras, Cyrtoceras and Lituites ; Gasteropoda, of 

 the genera Pleurotomaria and Murchisonia ; Brachiopoda, of the genera 

 Orthis and Strophomena ; Lamellibranchiata, of the genera Tellinomya 

 and Ambonychia ; and zoophytes or corals in fragments. 



The Pleurotomaria subconiva, Oncoceras pandion, Tellinomya cuneata, 

 Ormoceras tenuifilum, Tellinomya ventricosa, and species of Orthocera and 

 Ambonych-ia, are the fossils occurring in the greatest abundance. The 

 casts of some of these come out in great perfection. 



^Economical Geology. 



Building Stone. All three of the above described formations or divi- 

 sions of the Trenton rocks furnish stone adapted for building and ordi- 

 nary mason work. Especially is this true of the Galena limestone. 

 The quarries at Harlem and Cherry Valley furnish excellent materials 

 for solid and massive railroad masonry. The public school building in 

 the city of Rockford is a model of architectural beauty, and solid impo- 

 sing grandeur. No painter's art could improve its present rich, warm 

 color. The beautiful cream colored residences scattered about the city, 

 present an equally striking appearance. When dressed and laid up of 

 equal thickness, nothing can excel the effect of these stone residences. 

 We have heard much said of the beauty and aristocratic appearance of 

 brown-stone fronts in other wealthy cities ; but no stone ever quarried. 



